L-30-100, Rev 2 to Design Rept for Recirculation Sys Weld Overlay Repairs & Flaw Analysis at Brunswick Steam Electric Plant Unit 1

Rev 2 to Design Rept for Recirculation Sys Weld Overlay Repairs & Flaw Analysis at Brunswick Steam Electric Plant Unit 1

ML20132D484
Person / Time
Site:	Brunswick
Issue date:	09/30/1985
From:	Gustin H, Kleinsmith M, Wenner T NUTECH ENGINEERS, INC.
To:
Shared Package
ML20132D476	List: L-30-100, Rev 2 to Design Rept for Recirculation Sys Weld Overlay Repairs & Flaw Analysis at Brunswick Steam Electric Plant Unit 1 ML20132D475
References
CPL-30-100, CPL-30-100-R02, CPL-30-100-R2, NUDOCS 8509300186
Download: ML20132D484 (34)

Text

_ - . .

NUTECH -

CONTROLLED CPL-30-100 Revision 2 September 1985 CPLO30.0100 DESIGN REPORT FOR RECIRCULATION SYSTEM WELD OVERLAY REPAIRS AND FLAW ANALYSIS AT BRUNSWICK STEAM ELECTRIC PLANT UNIT l c

Prepared fort Carolina Power and Light Company Prepared by:

NUTECH, Inc.

San Jose, California ll Prepared by: Reviewed by:

C, hau, v M. E. Kleinsmith H. L. Gustin, P.E.

Consultant I Project Engineer Approved by: Issued by:

9 A- - p [

T. J. Wenner, P.E. D. K. dshida,P.E.

Engineering Manager Project Manager Date ifill85 8509300186 850925 PDR ADOCK 05000325 P PDR

~

REVISION CONTROL SHEET .

TITLE: Design Report for DOCUMENT FILE NUMBER: CPLO30.0100 Recirculation S' stem y Weld Overlay Repairs and Flaw Analysis at Brunswick Steam Electric Plant Unit 1 H. L. Gustin, P.E./ Project Engineer N AME / TITLE INITI ALS M. E. Kleinsmith/ Consultant I N AME/ TITLE fr rf iNITI'A LS N. G. Cofie/ Senior Consultant A/ dd.

N AME / T'TLE INITI A LS N AME / TITLE INITI ALS AFFECTED DOC PAEPAAE0 ACCUAACY CRITE RI A R4 PAGEtS AEV BY ?OATE CHECK SYlOATE CHECK 8Y / DATE i-vi 0 Nd %YdF ^/4c </r/sf gf4 9/3/yf Initial Issue 1-28 0 @ct "/MJ ucc 9/5/sr ///d T[3/'I 23 1 Sd 9/ich7 pp $/../d Tf<0,ft? Added NOTE, revised nek g/nr "

8,17 2 ,;C c Slo /rf M 9/11/6f 'A ed R erence 9, 20,28 2 ncW VM/8f use. 9/o/ts g $[g[gf revised stresses and crack growth prediction 11 vi PAGE OF li a . ; t .1 A EV .1

CERTIFICATION BY REGISTERED PROFESSIONAL ENGINEER I hereby certify that this document and the calculations con-tained herein were prepared under my direct supervision, or reviewed by me, and to the best of my knowledge are corr'ect and complete. I ~further certify that, to the best of my knowledge design margins required by the original Code of Construction have not been reduced as a result of the repairs addressed herein. I am a duly Registered Professional Engi-neer under the laws of the State of North Carolina and am competent to review this document.

.iiin ,e,,,,

/' W C ARO[' #*, Certified by:

/S(Q*Gi?J,./ ,',,

f [ SEAL I i i 12504 I!

H. L. Gustin, P.E.

Registered Professional Engineer State of North Carolina Ragistration No. 12504 CPL-30-100 111 .

Revision 2 nutggh

. . . _ , . . =_ . .

TABLE'OF CONTENTS Page  ;

LIST OF TABLES V LIST OF FIGURES vi 1

.l .0 INTRODUCTION 2.0 REPAIR DESCRIPTION 7 3.0 EVALUATION CRITERIA 13 3.1 Weld Overlay Repair Criteria 13 3.2 Flawed Pipe Analysis Criteria 14 4.0 LOADS 15 4.1 Mechanical, Internal Pressure, and Thermal Loads 15 4.2 Weld Overlay Shrinkage - Induced Loads 15 5.0 EVALUATION METHODS AND RESULTS 18 5.1 Code Evaluation - Section XI 18 5.2 Fracture Mechanics Evaluation 19 5.3 Overlay Shrinkage Effect on Recirculation System .

20 5.4 Low Material Toughness Concerns 21 6.0

SUMMARY

AND CONCLUSION 25

7.0 REFERENCES

27

.I I

CPL-30-100 iv .

Revision 2 l

t i,

LIST OF TABLES Table ' Title Pace t

1.1 Brunswick Unit 1 Flaw Disposition 2 l

)

h j 2.1 Weld overlay As-Built Dimensions 9 ,

l 1

4 4.1 Summary of Total Stresses 17  :

, i l 5.1 Summary of Shrinkage Stresses at Recirculation i i System Flaw Locations 23 -

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i 4

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2 1

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! CPL-30-100 v . ,

Revision 2

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LIST OF FIGURES Figure Title Page i

i 1.1 Conceptual Drawing of Recircu'lation System 5 1.2 Weld Overlay Dimension Definition 6

! 2.1 Configuration of Safe End-to-Pipe Weld Overlay 10 2.2 Configuration of 12" Elbow-to-Pipe Weld Overlay 11 i .

] 2.3 Configuration of 28" Elbow-to-Pipe Weld Overlay 12 4

S.1 Brunswick Unit 1 Recirculation System Piping Model 24 I

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1.0 INTRODUCTION

This report summarizes analyses performed by NUTECH to evaluate flaw indications and weld overlay repairs in l

the Recirculation System at Carolina Power and Light Company's Brunswick Steam Electric Plant Unit 1 (Brunswick 1). The flaw indications addressed in this report were detected during the summer 1985 refueling i outage inspection.

Flaw indications were identified adjacent to 23 welds in the Recirculation System. One flaw indication detected by ultrasonic (UT) examination was determined to be ac-ceptable without repair for at least the next 18 months. The remaining flaw indications were repaired by I

application of weld overlay. The purpose of each over-

lay is to arrest any further propagation of intergranu-lar stress corrosion cracking (IGSCC), and to restore original design saf ety margins to the weld. All flaws are in Type 304 stainless steel material. Figure 1.1 l shows the location of these flaw indications. Table 1.1 contains a description of each flaw indication an'd the disposition of each.

r CPL-30-100 1 .

Revision 2

r Table 1.1 BRUNSWICK UNIT 1 FLAW DISPOSITION overlay Desion (in.)f Tmin/No. Pipe a L2 -Size Weld No. Flaw of Layers L1 A8 Circumferential N/A N/A N/A 28" '

2.25"x25%,

upstream 12-AR-A2 Axial, 0.4", 2 layers 1.5 1.5 12" -

upstream D

$ 12-AR-A3 Circumferential, 0.250" 1.5 1.5 12" 1.75"x35%,

i upstream ,

12-AR-B3 Axial, 0.5", 2 layers 1.5 1.5 12" downstream i

12-AR-C2 Circumferential, 0.260" 1.5 1.5 12" 0.6"x50%,

downstream 12-AR-C3 Axial, 0.4", 2 layers 1.5 1.5 12" downstream i 12-AR-D2 Axial, 0.60", 2 layers 1.5 1.5 12" I upstream D 12-AR-D3 -Axial,0.3f5", 2 layers 1.5 1.5 12"

downstream i 12-AR-D4 Circumferential, 0.220" 1.5 0.625 12"

' 2.0"x35%,

i upstream i

12-AR-E3 Axial, 0.4", 2 layers 1.5 1.5 12"

' downstream 12-BR-F2 Axial,0.7g", 2 layers 1.5 1.5 12" downstream 12-BR-G2 Circumferential, 0.220" 1.5 1.5 12" 1.125"x25%,

upstream l

l 4

CP L- 30-100 2 ^.!

Revision 2 1

Table 1.1 BRUNSWICK UNIT 1 FLAW DISPOSITION (continued)

Overlay Design (in.)f Tmin/No. Pipe a of Layers L1 L2 Size Weld No. Flaw 12-BR-G3 Axial, O g8" 2 layers 1.5 1.5 12" upstream 12-BR-G4 Axial, 0.5", 2 layers 1.5 0.60 12" b

upstream 12-BR-H2 Axial, 0.4", 2 layers 1.5 1.5 12" D

downstream 12-BR-H3 Axial, O g 5", 2 layers 1.5 1.5 12" upstream f

12-BR-J2 Axial, O g6" 2 layers 1.5 1.5 12" upstream 12-BR-J3 Circumferential, 0.230" 1.5 1.5 12" 4"x60%,

downstream 12-BR-K2 Axial C 2 layers 1.5 1.5 12" 12-BR-K3 Axial,Oj75" 2 layers 1.5 1.5 12" upstream 12-BR-K4 Axial, O g4" 2 layers 1.5 0.55 12" upstream 28-A4 Axial, O 6", 2 layers 1.6 1.6 28" upstream d 28-B4 Axial, 0.6" 2 layers 1.5 1.5 28" x25%, upstream

• CPL-30-100 3

, Revision 2 g

i Table 1.1 BRUNSWICK UNIT 1 FLAW DISPOSITION (continued) a Flaw size used in designing overlay b Flaw depth assumed 100%

c Leaking flaw undetected by UT, flaw assumed axial .7"x100%

d Circumferential flaws present did not require overlay; flaw depth assumed 100%

• Circumferential flaws present did not require overlay f

See Figure 1.2 for definition of weld overlay dimensions CPL-30-100 -4 .

Revision.2 nutagh

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PATENT ADPLIED FOR Figure 1.2 WELD OVERLAY DIMENSION DEFINITION CPL-30-100 6 .

Revision 2 nutggh

2.0 REPAIR DESCRIPTION The UT flaw indications requiring repair were remedied 4

by establishing additional " cast-in-place" pipe wall thickness with weld metal deposited 360 degrees around and to either side of the existing weld, as shown in Figures 2.1 through 2.3. The weld-deposited band over the cracks provides, as a minimum, wall thickness equal to that required to meet the requirements of Reference ,

1, as modified by Reference 2. NRC Generic Letter 84-11 (Reference 2) requires that the first weld overlay layer not be included in the design thickness. A favorable compressive residual stress distribution results from overlay application, which will tend to inhibit further.

crack initiation or growth. The deposited weld metal is type 308L, which is resistant to IGSCC propagation.

Table 2.1 presents design and as-built inf ormation for the overlay repairs applied to Brunswick 1.

All weld overlay repairs were inspected using non-destructive examination. Non-destructive examination of the weld overlays consisted of the following:

I

! 1) Surface examination of the first weld overlay layer by the liquid penetrant examination technique in i accordance with ASME Section XI (Reference'l).

i CPL-30-100 7 ~,

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2) Delta ferrite measurement of the first layer, using a Severn gauge.

3) Surface examination of the completed weld overlay by the liquid penetrant examination technique in accordance with ASME Section XI (Reference 1).

4

4) Volumetric' examination of the completed weld over-l '

lay by the ultrasonic examination technique in accordance with ASME Section XI (Reference 1).

l 5) Volumetric examination of the weld overlay.to pipe I

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bond and existing circumferential pipe weld by the ultrasonic examination technique in accordance with i

l recommendations outlined in the EPRI interim report  %

dated April 1985, " Examination of Weld Overlayed l Pipe Joints" (Reference 9).

i

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I i CPL-30-100 8 .

Revision 2

I Table 2.1 l

WELD OVERLAY AS-BUILT DIMENSIONS i

j Design Tmin/ As-Built As-Built {

l Weld I.D. Pipe Size No. of Layers Thickness Lencth 1,

1 12-AR-A2 12 2 layers 0.303 3.453 l 12-AR-A3 12 0.250 0.419 3.188 i

j 12-AR-B3 12 2 layers 0.398 3.43 1

i 12-AR-C2 12- 0.260 0.435 3.640 l 12-AR-C3 12 2 layers 0.435 .3.037 12-AR-D2 12 2 layers 0.296 3.170 6

] 12-AR-D3 12 2 layers 0.317 3.075 i

! 12-AR-D4 12 0.220 0.404 2.225 i 12-AR-E3 12 2 layers 0.373 3.064 12-BR-F2 12 2 layers 0.328 3.453 i 12-BR-G2 12 0.220 0.418 3.288 i

j 12-BR-G3 12 2 la'yers 0.468 3.050 i

j 12-B R-G4 12 2 layers 0.205 2.923 l-j 12-BR-H2 12 2 layers 0.280 3.482 ,

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12-BR-H3 12 2 layers 0.465 3.175

{ 12-BR-J2 12 2 layers 0.290 3.101 f 12-BR-J3 12 0.230 0.447 3.115 12-BR-K2 12 2 layers 0.410 3.110 f

12-BR-K3 12 2 layers 0.320 3.250 j 12-BR-K4 12 2 layers 0.213 2.425 {

28-A4 28 2 layers 0.140 3.525 i

l 28-B4 28 2 layers 0.163 3.72 l

• Exclusive of first layer thickness

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I CPL-30-100 9 Revision 2 i 1 f , _ __._, _ . _ . _ ,.-. _ , _ _ _ _ _ . _ , . _ _ _ _ _ _ . _ . _ _ _ _ . - . _ _ _ _ _ _

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" PUP" PIECE TO SAFE END TO PIPE WELD NOZZLE WELD (1) MINIMUM THICKNESS VARIES, BUT DOES NOT

$ INCLUDE FIRST LAYER THICKNESS PATENT APPLIED FOR (2) DIMENSION VARIES DEPENDENT UPON EXTENT OF INCONEL Figure 2.1 CONFIGURATION OF SAFE END-TO-PIPE WELD OVEHLAY

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TYM 300L WELD CVERLAY a

1.5 MIN -

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Revision 2

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TYPE XISL WELD OVERLAY 1.5 MIN =

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(1) MINIMUM THICKNESS OF 2 LAYERS DOES

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3.0 EVALUATION CRITERIA This section describes the criteria that are applied in this report to evaluate the acceptability of the weld overlay repairs and flawed pipe analysis. A Section III stress evaluation was not performed as part of.this analysis since the Section XI evaluations inherently satisfy Section III requirements.

3.1 Weld Overlay Repair Criteria Due to the nature of these repairs, the geometric configu-ration is not directly covered by Section III of the ASME Boiler and Pressure Vessel Code, which is intended for new construction. However, materials, fabrication procedures, and Quality Assurance requirements meet applicable sections of the original construction code. In addition, since con-ditions conducive to IGSCC led to the need for repairs, IGSCC-resistant materials have been selected for the weld overlay repairs.

A conservative method was used to demonstrate the adequacy of weld overlay repairs. All relevant UT indications were assumed to be through-wall for their measured length. The weld overlays were then designed such that the net section CPL-30-100 13 ~.

Revision 2

limit load requirements of Reference 1 were satisfied, in addition to the requirements of Reference 2.

3.2 Flawed Pipe Analysis Criteria Weld 28-A8 contained a circumferential' flaw determined to be 2.25" long with a depth of 20%. Due to its small initial length, the end-of-cycle allowable flaw depth defined in Table IWB-3641-1 of ASME Section XI (Refer-ence 1) is 75% of the pipe wall thickness.. The NRC's Generic Letter 84-11 (Reference 2) modifies this depth by a factor of 2/3. The end-of-cycle allowable flaw depth is defined to be 50% of the pipe wall thickness, for the purpose of this analysis.

The upcoming cycle length is 18 months. Therefore the flaw must be shown to be acceptable without repair for at least the next 18 months, utilizing the crack growth law presented :in Section 5.2.

i i

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CPL-30-100 14 ,

Revision 2

o

.. i 4.0 LOADS The loads considered in the evaluation of UT flaw indi-cations included. mechanical loads, internal pressure loads, dif ferential thermal expansion loads, and weld overlay-induced shrinkage loads. Mechanical and inter-nal pressure loads are used in designing weld overlays and are described in'Section 4.1. Differential thermal and- overlay shrinkage-induced loads are -included for crack growth predictions. The weld overlay shrinkage-induced loads are explained in'Section 4.2.

4.1 Mechanical, Internal Pressure, and Thermal Loads Internal pressure information for the Recirculation Sys-tem was obtainedifrom Reference 3. Deadweight, thermal and seismic loads applied to the Recirculation System welds were obtained from Reference 4. Calculated stresses are included in Table 4.1.

4.2 Weld Overlay Shrinkage - Induced Loads Weld overlays cause a small amount of axial shrinkage beneath the overlay. The resulting loads are manifested as bending stresses in the remainder of the piping sys-tem. Shrinkage loads in the Recirculation System were 4

CPL-30-100 15 -~

Revision 2 nutagh

calculated using a PISTAR (Reference 5) piping model, weld overlay shrinkage is discussed further in section 5.3.

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l CPL-30-100 16 -\

Revision 2 nutgch  !

• t Table 4.1.

SUMMARY

OF TOTAL STRESSES Maximum Stress (PSI) Total Stress (PSI)

Deadwe ight + Crack Wol Weld No. Thermal Seismic Pressure Growth Design 28-A8 2358 1141 7346 9704 8487 l 12-AR-A2 -- --

• 14030 14030 '

14030 AR-A3 8960 2150 6343 15303 8493 l AR-B3 -- --

• 14030 14030 14030 12-AR-C2 6231 1463 6308 12539 7771' l 12-AR-C3 -- --

• 14030 14030 14030 12-AR-D2 -- --

• 12649 12649 12649 12-AR-D3 -- -- *14030 14030 14030 ,

4 12-AR-D4 10049 2722 6318 16367 9040 12-AR-E3 -- --

• 12649 12649 12649 12-BR-F2 -- --

• 12649 12649 12649 12-BR-G2 5608 738 6568 12176 7306 l 12-BR-G3 -- --

• 12649 12649 12649 12-BR-G4 -- -- *10768 10768 10768 12-BR-H2 -- --

• 10696 10696 10696 12-BR-H3  :-- --

• 14030 14030 14030 12-BR-J2 -- --

• 12649 12649 12649 12-BR-J3 8769 1259 6339 15108 7598 12-BR-K2 -- --

• 14030 14030 14030 12-BR-K3 -- --

• 12649 12649 12649 12-BR-K4 -- --

• 10768 10768 10768 28-A4 -- --

• 12880 12880 12880 28-B4 -- --

'*13417 13417 13417 s

• Circumferential stress due to pressure only CPL-30-100 17 -,

Revision 2 nutggb

5.0 EVALUATION METHODS AND RESULTS The flawed welds shown in Table 1.1 were identified by UT inspections during the summer 1985 refueling outage inspection at Brunswick Unit 1. These flawed welds were evaluated based upon the criteria of Section 3-to deter-mine whether an overlay was necessary to meet the re-quirements of Reference 1 and 2. Only one flawed weld (28-A8) was found to meet the' requirements of References l'and 2 without an overlay repair.

The application of weld overlays imposes a small amount of axial shrinkage at the weld location,which produces secondary stresses on the remainder of the piping sys-tem. The analysis made to determine the magnitude of this effect at each weld location and to address its sig~nificance is discussed in Section 5.3.

5.1 Code Evaluation - Section XI All weld overlays were designed assuming flaws were through-wall for their measured length. Welds contain-ing axial flaws only or axial flaws with very small ,

circumferential flaws (as in welds 28-A4 and 28-B4) require only a leakage barrier. This leakage barrier consists of two layers of weld overlay material, with an CPL-30-100 18 .

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l Revision'2 nutagh

additional layer as required by Reference 2. Circumfer-ential flaws in 12" pipe were overlay repaired in ac-cordance with Reference 1. All overlay designs restore the safety margins required in Section IWB-3640 of ASME Section XI (Reference 1). The flaw in weld 28-A8 meets these requirements without repair and will not violate them for at least the next 18 months.

5.2 Fracture Mechanics Evaluation The allowable end-of-cycle flaw depth was determined from References 1 and 2.- Calculation of crack growth '

due to IGSCC was based on Reference 6 and NUTECH's computer program NUTCRAK (Reference 7). Input to NUTCRAK included the as-measured flaw depth, a con-servetive residual stress distribution, and the follow-ing conservative crack growth law.

3.59 x 10 -8 g 2.161 (Reference 3) hf =

Where da = differential crack depth (in) i dt =' differential time (hrs) . f K = stress intensity at the crack tip (ksi Vin)

CPL-30-100 19

• i Revision 2 O

c

Based on this conservative analysis, it was predicted that the flaw in weld 28-A8 would not exceed the end-of-cycle allowable crack depth for at least 22 months. <[l 5.3 Overlay Shrinkage Effect on Recirculation System The effects of the radial shrinkage are limited to the region adjacent to and directly underneath the weld overlay. Based on Reference 8, the stress due to the radial shrinkage is less than the yield stress at dis-tances greater than about.four inches from either end of the overlay.

The effect of the axial weld shrinkage on the Recircula-tion System was evaluated with the NUTECH computer pro-gram PISTAR (Reference 5) using the piping model pre-sented in Figure 5.1. The' measured shrinkages due to all overlays applied this outage, as well as those due to previously applied overlays, were imposed as boundary conditions on this model. Since the ASME Code does not limit weld residual stress, all stress indices were set equal to 1.0.

The PISTAR program was used to elastically calculate stress due to weld shrinkage. The maximum calculated stress for an IGSCC susceptible weld was 18.1 ksi at l

CPL-30-100 20 i Revision 2 ~l 1

3 e

nozzle weld N2D (weld 12-AR-D4). This weld is a 12" safe-end-to-nozzle weld on a recirculation riser, and f was overlay-repaired. None of the stresses reported in i Table 5.1 take into account the increased membrane due l to overlay. Table 5.1 gives the ' shrinkage stress for all welds in the recirculation system found to have  ;

j Since weld shrinkage-induced stresses are not flaws.

3

?

limited by the ASME Code, the Code acceptability of i these welds is not in question. It is judged that r

stresses of the-magnitude calculated will have negli-gible effect on the integrity or IGSCC susceptibility of these welds.

i 5.4 Low Toughness Material Concerns F

Recently, concerns have been raised that the toughness

] .

of weld metal in stainless steel butt-welds deposited by

! flux shielded processes may be substantially lower than that of the surrounding metal. 'Potentially, this could i

lead to brittle failure of the butt weld material at an

~i applied load appreciably below the net section collapse l lead of the adjacent piping material. As of the date of this report,-there is no formal regulatory or Code guid-

ance on this issue.

i i

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. CPL-30-100' 21 ^. l l Revision 2 i l

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NUTECH reviewed the weld overlays and unrepaired flaw at Brunswick 1 to address this issue. Most of the repaired flaws are oriented axially and are thus not affected by the toughness concern. -The weld overlay as-built thick-nesses of welds containing~circumferential flaws are large enough to adequately repair 360*x100% flaws, ex-cluding credit for the first overlay layer, as required by Reference 2. Therefore, no credit for the butt weld material need be taken. Finally, the unrepaired. flaw in weld 28-A8 is very short'and shallow and is thus not of i

concern.

I 1

4 9

4

! CPL-30-100 22

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Revision 2 1

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Table 5.1

SUMMARY

OF SHRINKAGE STRESSES AT RECIRCULATION SYSTEM FLAW LOCATIONS Shrinkage Weld Number Overlay Stress (PSI) 28-A8 No 176 12-AR-A2 Yes 1306 12-AR-A3 Yes 1410 4 12-AR-B3 Yes 557 I 12-AR-C2 Yes 1909 4

12-AR-C3 Yes 2651 12-AR-D2 Yes 6350 i- 12-AR-D3 Yes 4255 12-AR-D4' Yes 18067 12-AR-E3 Yes 5422 12-BR-F2 Yes 743 12-BR-G2 Yes 3348

12-BR-G3 Yes 1230 12-BR-G4 Yes 8923 i 12-BR-H2 Yes 989 12-BR-H3 Yes 2248 12-BR-J2 Yes 633

12-BR-J3 Yes 812

12-BR-K2 Yes 2534 1

12-BR-K3 Yes 2216 12-BR-K4 Yes 1125 28-A4 Yes 195 28-B4 Yes 191 12-AR-A4* Yes 879 12-AR-B2* Yes 282

12-AR-84* Yes 558 12-AR-E2* Yes 3358 12-BR-F4*

• Yes 1008 12-BR-H4* Yes 6989 4 28-A14* Yes 123 28-A15* Yes 218 28-88* Yes 189

• Overlay repaired during a previous outage NOTE: Bypass loop weld 4A-10 was also overlay repaired. Its shrinkage will not affect the remainder of the system. ,

Shrinkage stress present at this weld is less than 100 psi.

CPL-30-100 23

• Revision 2 .

HIGHEST STRESS LOCATION

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i ... ,

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in f. hm Ni. - '

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.n FCPL85.03

- Figure 5.1 BRUNSWICK UNIT 1 RECIRCULATION SYSTEM PIPING MODEL CPL-30-100 Revision 2 24 nutg_qh

6.0

SUMMARY

AND CONCLUSION Evaluation.of the repairs to the Recirculation System reported herein shows that the resulting stress levels are acceptable for all design conditions. The stress i

levels have been assessed from the standpoint of load i

capacity of the components and the resistance to crack growth.

i Acceptance criteria for the analyses have been estab-lished in Section 3.0 of this report which demonstrate that:

1. Overlay repaired welds meet margins of safety in- 'I

~

herent in IWB-3640 of ASME Section XI (Reference 1).

2. The one flawed weld which did not require weld overlay repair-will not exceed the allowable flaw size of Reference 1 as modified by. Reference 2 over at.least the next 18 months.

l l

Analyses have been performed and results are presented which demonstrate that the repaired welds satisfy these

- criteria by a large margin. Analyses have also been CPL-30-100 25 Revision 2

f performed which demonstrate that the unrepaired weld satisfies these criteria by a large margin. ,

}

Fu r t he rmo re , it is concluded that IGSCC experience in the Reactor Recirculation System at Brunswick Unit 1 does not increase the probability of a design basis pipe rupture at the plant. This conclusion expressly con-t~

siders the nature of the cracking which has been ob-I served at Brunswick Unit 1, and the likelihood that other similar cracking may have gone undetected.

I Finally, the possibility that butt welds with extremely low toughness exist at Brunswick 1 nas been considered and found not to violate acceptance criteria.

\

t I,

i I

CPL-30-100 26 Revision 2 ritit99.I.l.

I I

7.0 REFERENCES

i

1) ASME Boller and Pressure Vessel Code,Section XI,

' 1983 Edition with Addenda through Winter 1984, Paragraph IWB-3640, " Acceptance Criteria for Austenitic Steel Piping."

2) NRC Generic Letter 84-11, dated April 19, 1984,

! File No. CPLO30.0012.

I

{

3) General Electric Design Specification 22A1417, Revision 2, File No. CPLO30.0012.

4) General Electric " Brunswick Steam Electric Plant Unit 1 Recirculation Pipe System Stress Reanaly-sis," 6/11/85, File No. CPLO30.0012.

5) NUTECH Computer Program PISTAR, File No.

08.003.0300, Version 3.2.

6) NUREG 1061, Vol. 1, " Investigation and Evaluation of Stress-Corrosion Cracking in Piping of Boiling Water Reactor Plants," Second Draft, April 1984.

- 7) NUTECH Computer Program NUTCRAK, Version 2.0.2, File No. 08.039.0005.

CPL-30-100 27

~

Revision 2 nutggh

I

8) NUTECH Report NSP-81-105, Revision 2, " Design Report for Recirculation Safe End and Elbow Repairs, Monticello Nuclear Generating Plant,"

December 1982 Elle No. 30.1281.0105.

9) EPRI Interim Report, " Examination of Weld Overlayed

<g 1

Pipe Joints," dated April 1985, RP1570-2.

I li s.

CPL-30-100 28 Revision 2 nutRch